The invention is directed to the improved corrosion resistance of steel reinforced concrete.
Concrete structures containing embedded reinforcing bars are widely used. When these structures are exposed to salts over long periods of time severe corrosion of the reinforcing bars occurs. The corrosion products expand and crack the concrete. This causes massive failure of the structure.
One method of protecting these structures is to coat the reinforcing bars. This method can only be used on new structures. Another method is to add a corrosion inhibitor to the concrete before it is poured. Again this can be used only on new structures. There are thousands of preexisting concrete structures in this country that are corroding.
One method of protecting the embedded steel in these structures is by cathodic protection, see Corrosion 83, Paper No. 179, The International Forum, Apr. 18-22, 1983. The negative pole of a direct current source is connected to the steel to be protected. The positive pole or anode is connected to the exterior of the concrete structure.
One of the problems associated with this process is getting an even distribution of current to the surface of the reinforcing metal to be protected. The prior art attempts to solve this problem by adding coke or other conductive materials to the concrete. This method is expensive and changes the mechanical properties of the concrete. Another method is to paint the concrete with a coating containing a conductive pigment. Paints of prior art containing conductive pigment are hard to apply and lose adhesion to the concrete when subjected to the combined stress of current flow and ambient moisture conditions.